1. Technical Field of the Invention
The present invention relates to thermoplastic hollow articles that are excellent in rigidity and impact absorption qualities, as well as to the manufacturing process for producing the hollow articles.
2. Background Art
Hollow articles are well known in the art and used in a variety of industries and applications. These plastic hollow articles are lightweight, strong, and relatively inexpensive to manufacture using injection or blow molding techniques.
There are numerous examples of products that employ hollow articles, such as ducts, panels, or housings for electronics, appliances, automobiles, and house wares. In many homes these hollow articles are found in walls, partitions, and panels, such as entrance doors, and indoor air conditioning ducts. Furniture is also manufactured with hollow structures, and includes top plates of desk, partition panels, and bookshelf panels.
In the appliance sector, housings of some of the components are hollow such as used for refrigerators and televisions. The hollow articles are also used in office equipment, such as the housings of copy machines, facsimile machines and computer peripherals.
Panels and ducts of dwelling facilities, furniture panel, housing of electric household appliances, housing of office equipment and automotive parts are often required to have a high rigidity. Hollow articles used in such applications are manufactured in integral structures combining a first wall and a second wall by means of a rib linking them mutually within a hollow space. In cases where the appearance is important on both face and back surfaces, a structure termed an xe2x80x9cinner ribxe2x80x9d is employed. Thus, the first wall and the second wall are projected, in blow molding, until a part of the second wall contacts with a wall to be linked integrally within the hollow space there between.
The automobile industry uses hollow articles because of the mechanical properties and weight characteristics. Automotive parts include console box lid, hood, door panel, and air conditioning duct. For example, in order to assure the rigidity as a product or to protect the crew from impact of collision, an automotive roof side duct is disposed near both sides of ceiling as explained in Japanese Patent Application Laid-Open No. 2000-43541.
The automobile industry is particularly interested in increasing the safety of the vehicles, and at a minimum, complying with the certain safety guidelines. According to the Federal Motor Vehicle Safety Standards (FMVSS), the hollow articles must have a minimum level of impact absorption. The guidelines are established under the Department of Transportation by the National Highway Traffic Safety Administration. There are a number of guidelines and requirements, including FMVSS 201 that addresses occupant protection in interior impact. There are other guidelines that describe related topics such as resistance to roof crushing. Head injuries are calculated according to a xe2x80x98heading injury criteriaxe2x80x99 (HIC) that is obtained from the deceleration of the head during the duration of the impact. These federal standards must be satisfied in order for vehicle to enter the U.S. market. And, these regulations are continuously being updated as new innovations and features result in improved safety characteristics.
There are many studies that demonstrate that significant head injuries and trauma occur when the driver or passengers head strikes the interior roof and side panels. A rigid interior wall offers little impact absorbing qualities when struck by a human head. There are a number of techniques used to impart some shock absorbing qualities into the roof and interior panels, but the strict government standards continue to increase and demand greater safety thresholds. The use of ceiling air bags and structural modifications to the support elements are designed to address the impact absorbing qualities, however there are issues such as cost and manufacturability that limit the wide-spread use of such features.
As shown in prior art FIG. 11, the inner rib of a roof side duct is integrally formed by blow molding, wherein an inside wall 101 facing a ceiling interior member 107 and an outside wall 102 facing an inner panel 106 of car body confront each other. A flat impact absorbing rib 103 is disposed along the longitudinal direction in a space 110 between the inside wall 101 and outside wall 102. A general manufacturing method of this roof side duct is explained by referring to FIGS. 12a, 12b, and FIG. 13.
Prior art FIG. 12a shows a molten parison 300 being poured into opened split molds 201, 202, and then the molds are closed. Next, a rib forming plate 203 is projected toward the second mold 202, and a neck 303 is formed in the area of first wall 301 of the parison, and its leading end is pressed tightly to the area of second wall 302. Then, as shown in FIG. 12a, the rib forming plate 203 is pulled in, the pressurized air is introduced into the parison 300, and is inflated into a shape along the cavity by the internal pressure of the pressurized air, and the neck 303 is pressed and deformed in the direction of the arrows, while confronting walls are fused integrally, so that an impact absorbing rib 304 is formed.
According to the prior art, as shown in FIG. 13, when pulling in the rib forming plate 203, after projecting the rib forming plate and forming a neck at first wall side of the parison, the neck is dragged in the backward direction of the rib forming plate 203, or is elongated by the blow pressure in the blow process, and the wall thickness and width of the flat rib formed as the confronting walls of the neck are compressed from both sides by internal pressure of the pressurized air are decreased. Thus, at portion 305 the inner rib is reduced in wall width and the shape, and the dimensions and wall thickness of the flat rib are not uniform on the whole. As a result, the rigidity and other mechanical strength of the impact absorbing rib 304 are lowered, and the duct having sufficient impact absorbing performance is lessened. Furthermore, the varying thickness of the inner rib results in some inconsistency in impact absorbing qualities. In the described application, such a product may result in inadequate protection in the event of a collision. Other applications may result in improper rigidity and strength and at the very least, inconsistency in the produced hollow article.
What is needed is a hollow article with a rib of uniform shape, dimensions and wall width. The rib should have excellent mechanical strength and properties. In one embodiment, such as automotive, the hollow article with the rib should have impact absorbing qualities to protect the driver and passengers. The manufacturing method for such an improved hollow article should be cost-effective and have a low defect rate.
The invention is devised in the light of the problems of the prior art described herein. The present invention is a hollow article having an impact absorbing rib uniform in shape, dimensions and wall width on the whole, especially free from reduction of wall width of the inner rib, yet possessing proper rigidity and mechanical strength, and excellent impact absorbing performance.
Another aspect of the invention is to ensure compliance with the FMVSS 201 regulations addressing interior head injury criteria. According to FMVSS 201, the interior of the vehicle in the U.S marketplace must have a head injury criteria (HIC) of less than 1000. The value is determined by striking a dummy head of a certain mass into the regions of the vehicle interior at a certain speed and measuring the shock value. The present invention results in an article that is well within the federal guidelines. In addition, present invention has a greater consistency and repeatability as compared to prior art products that have a higher rate of failure of compliance. The prior art components are generally unable to satisfy the HIC standards, and therefore cannot pass the FMVSS 201 specifications. For example, the roof side ducts of the prior art were tested and the HIC was found to be approximately 1500, which is above the 1000 HIC threshold.
One object of the invention is a hollow article made of a thermoplastic resin and integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing, an integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib projecting from the second wall to the first wall, and a hollow rib adjacent to each of two side ends of the flat rib, wherein the flat rib and the hollow rib are fused to an inner side of the first wall.
A further object is the hollow article, wherein the hollow rib is tapered with a more narrow portion at the first wall. Additionally, wherein the integral rib is disposed along a longitudinal direction of the hollow article. And, wherein a plurality of the integral ribs are disposed at a mutual spacing.
An additional object is the hollow article, wherein the integral rib is disposed in an impact action direction. Also, wherein the hollow article is an automobile component
An object of the invention is a hollow article made of thermoplastic resin, integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing, an integral rib disposed between the first wall and the second wall, wherein the integral rib comprises a first flat rib projecting from the first wall to a fusion portion, a first hollow rib adjacent to each of two side ends of the first flat rib, a second flat rib projecting from the second wall to the fusion portion, a second hollow rib adjacent to each of two side ends of the second flat rib, wherein the first flat rib and the second flat rib are fused to each other at the fusion portion, and wherein the first hollow rib and the second hollow rib are fused to each other at the fusion portion.
Another object is the hollow article, wherein the first hollow rib and the second hollow rib form a combined concave hollow rib. Also, the hollow article, wherein the integral rib is disposed along a longitudinal direction of the hollow article. Additional objects of the invention include the hollow article, wherein a plurality of the integral ribs are disposed at a mutual spacing, and also wherein the integral rib is disposed in an impact action direction.
An object of the invention is a method of blow molding a hollow article having a first wall and a second wall confronting across a spacing, with an integral rib disposed between the first wall and the second wall, comprising the steps of opening a split mold, wherein the split mold has a first mold half with a cavity, a slide core and a pair of support cores on either side of the slide core, and a second mold half with a cavity, a slide core and a pair of support cores on either side of the slide core. Extruding a parison of molten thermoplastic resin between the split mold and closing the split mold, thereby deforming the parison with each sliding core and each of the pair of support cores and forming a first recess and a second recess, wherein a leading end of the first recess and a leading end of the second recess are fused. Next, retracting each of the slide cores and introducing a pressure substance into the parison and inflating the parison along a cavity surface of the split molds and the support cores and forming the integral rib between the first wall and the second wall, wherein the integral rib comprises a pair of flat ribs and a pair of hollow ribs, and cooling the split mold, opening the split mold and removing the hollow article.
And additional object is the method of blow molding, wherein the step of retracting the slide cores is simultaneous with the step of introducing the pressure substance. Also, wherein the pressurized substance is a gas.
An object of the invention is a method of blow molding a hollow article having a first wall and a second wall confronting across a spacing, with an integral rib disposed between the first wall and the second wall, comprising the steps of opening a split mold, wherein the split mold has a first mold half with a cavity, and a second mold half with a cavity, a slide core and a pair of support cores on either side of the slide core, extruding a parison of molten thermoplastic resin between the split mold, closing the split mold, deforming the parison with the sliding core and the pair of support cores and forming a recess, wherein a leading end of the recess is fused to an inner surface of an opposing wall side. Finally, retracting the slide core, introducing a pressure substance into the parison, inflating the parison along a cavity surface of the split molds and the support cores and forming the integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib and a pair of hollow ribs, cooling the split mold, opening the split mold and removing the hollow article.
A further object is the blow molding method, wherein the step of retracting the slide cores is simultaneous with the step of introducing the pressure substance. Furthermore, wherein the pressurized substance is a gas.
An object of the invention is an apparatus for blow molding a hollow article from a thermoplastic resin, having a first wall and a second wall confronting across a hollow space, and an integral rib disposed for providing structural support and absorbing impact between the first wall and the second wall, comprising a split mold with a first mold half and a second mold half, a slidably engageable slide core for forming a flat rib disposed in at least one of the mold halves, a pair of support cores disposed on at least one of the mold halves for forming a hollow rib and adjacent to each of two side ends of the slide core, and a means of retracting the sliding core.
Additionally, the apparatus for blow molding, wherein the pair of support cores is integrally disposed in the mold halves. And, wherein the pair of support cores is retractable from within the mold halves. Finally, the apparatus for blow molding wherein a surface of the slide core is treated with fluorine film coating so as to slide smoothly with the parison.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.